Pioneering implant revives legs of paralysed men

Big step: movement is possible

(Image: Jianwei Yang/Getty Images)

They can’t quite walk. Yet. But four wheelchair-bound men who until recently were completely paralysed below the waist can now move their legs and toes and even lift up to 100 kilograms with their legs. Their spinal cords have been reawakened by electrical implants that revive the flow of information between limbs and brain. Such feats would previously have been unthinkable in people with spinal cord injuries.

“We think it’s a very large milestone,” says Claudia Angeli of the Kentucky Spinal Cord Injury Research Center at the University of Louisville. “There’s not been anything like this, and no hope previously for the most severely injured patients, so this is a very important step forward for them.”

Video: Spinal cord implant revives paralysed legs

The device – an array of electrodes – is implanted not at the point of injury, but in the still intact lumbosacral region of the spinal cord, which is the main information hub linking the brain to the lower limbs. Despite being crushed, Angeli says, the spinal cord and its associated nerve connections retain huge capacity to continue sending messages.

Souped-up implant

Angeli is now planning to test the device in a further eight people. She says that it might be possible to refine the implant so it allows for better coordination, possibly leading to walking. With this in mind, she is starting experiments in animals with an implant that has 27 electrodes instead of 16.

Angeli says the implant restores what in healthy people would be the resting potential of the spinal cord – the baseline electrical activity that keeps the cord alert, but which wanes through lack of use in people who are paralysed.

Once this background electrical impetus is restored artificially, the cord reawakens and can register the brain’s “intent” to move and convert this into fine movement at the motor neuron level. And by modulating the voltage for each individual and for each task, algorithms that optimise delivery of electrical activity for specific movements can be worked out and applied at will by the patients.

But the existing device has limitations, says Angeli. For example, the algorithms tend to be different for right and left legs or toes, so only one side can be moved at a time. The hope is that a more sophisticated device will be able to deliver algorithms simultaneously, and so coordinate movement in both legs to enable walking. Simple as it sounds, this remains a challenge.

Another boost for the men is that to varying degrees they have all recovered bladder, bowel and sexual function. “That really restores dignity,” says Roderic Pettigrew, director of the US National Institute of Biomedical Imaging and Bioengineering in Bethesda, Maryland.

Flash of light moves mouse muscles

A genetic tweak can make light work of some nerve disorders. Using flashes of light to stimulate modified neurons can restore movement to paralysed muscles. A study demonstrating this in mice lays the path for using such “optogenetic” approaches to treat nerve disorders ranging from spinal cord injury to epilepsy and motor neuron disease.

Optogenetics has been hailed as one of the most significant recent developments in neuroscience. It involves genetically modifying neurons to produce a light-sensitive protein, which makes them “fire”, sending an electrical signal, when exposed to light.

One stumbling block has been the fear of genetically manipulating the brain irreversibly. In the latest study, a group led by Linda Greensmith of University College London and Ivo Lieberam of King’s College London altered mouse embryonic stem cells in the lab before transplanting them into nerves in the leg – making them easier to remove if necessary.

The team inserted an algal gene that codes for a light-responsive protein into the stem cells. Then they added signalling molecules to make the stem cells develop into motor neurons, the cells that carry signals between the spinal cord and the rest of the body. They implanted these neurons into the sciatic nerve – which runs from the spinal cord to the lower limbs – of mice whose original nerves had been cut (Science, doi.org/r6w).

After waiting five weeks for the implanted neurons to integrate with the muscle, Greensmith’s team anaesthetised the mice, cut open their skin and shone pulses of blue light on the nerve. The leg muscles contracted in response. “We were surprised at how well this worked,” says Greensmith.

To make the technique practical for people, the researchers are developing a light-emitting diode in the form of a cuff that would go around the nerve, which could be connected to a miniature battery under the skin. Clare Wilson

This article will appear in print under the headline “Implant reawakens paralysed spines”